How to gain big muscles?

Weight Lifting: If you are looking to build muscle mass - high weight with lower repetitions.

Lift weights: Go to a reputable gym. Get a personal trainer or take a weight lifting class at a local community college - exercise daily and lift weights - eat healthy foods, avoid fast food, stay hydrated.

High protein/Carb: If you would like to gain muscle, the best diet is high-protein especially branched-chain Amino Acids as well as high complex carbohydrates diet. Make sure immediately after exercise which should include lifting weights you have about 15 g of simple sugar along with 20 g of protein ideally branched-chain amino acids. Also besides weights do some cardio so you don't gain fat in the abdominal area.